1. Field of the Invention
The present invention relates to a magnetic brush developing means in an electrophotographic copying machine and an electrostatic recording apparatus.
2. Description of the Prior Art
In a magnetic brush developing means, the developer containing magnetic powder is adsorbed on the non-magnetic holder having magnets arranged therein due to the magnetic force of said magnets. The developer carried in the shape of a brush on the non-magnetic holder is then brought into contact with the electrostatic latent image formed on a charge receptor at the developing position, thus said electrostatic latent image is developed.
There are two types of developer, one is a two-component developer consisting essentially of a non-magnetic toner and a magnetic carrier and the other is a one-component developer consisting essentially of a magnetic toner. One-component developer is further classified into a conductive magnetic toner and a dielectric magnetic toner. The development is made in a way that toner charged in the polarity opposite to the electrostatic latent image is electrostatically adsorbed to the electrostatic latent image. In a two-component developer, a toner is charged by the friction with a carrier and the toner with a smaller grain diameter adheres to a carrier with a larger grain diameter, thus a magnetic brush is formed. In a single-component developer, a conductive magnetic toner is charged by the injection of an electric charge or by an electrostatic induction and a dielectric magnetic toner is frictionally charged by the member that makes contact with the toner in a developing container or in the middle of the transportation.
As a non-magnetic holder to adsorb developer and to form a magnetic brush, there exist various types in a sleeve shape, a cylinder shape and an endless belt shape. Inside the holder, typically a plurality of magnet pieces are provided radially, or magnetic poles are arranged on the peripheral surface of a bar magnet. As a latent image holder, on the other hand, there exist a photosensitive receptor that is used for an electrophotographic copying machine and a dielectric to be used for an electrostatic recording apparatus and their shape spans over a drum shape, an endless belt shape, a plate shape and a sheet shape.
FIG. 1 shows a conventional magnetic brush developing means. Inside a cylindrical sleeve 1 that is a non-magnetic holder, there are aranged a plurality of magnet pieces 2 in a way that their polarity oppose each other and a magnetic field strength distribution shown in FIG. 2 is given on the sleeve 1, which causes earing of the developer 3, and either one or both of the sleeve 1 and magnet pieces 2 are rotated solidly in a direction of the arrow as shown. The toner 3 that ears moves on the sleeve 1 and further moves to the position of a charge receptor 5, namely, to the developing position after being made to a uniform height by the developer layer regulating plate 4. It is contacted to the surface of the charge receptor 5, which that moves at a constant speed, and develops electrostatic latent images continuously.
In this developing means, the ear of aforesaid developer 3 is soft and consequently the cohesion of aforesaid developer does not easily take place when contacting the charge receptor 5 or the developer layer regulating plate 4. Further, the electric chargeability of said developer is excellent because stirring of said developer takes place on the sleeve 1. However, due to the magnetic field generated on the sleeve 1, there has been a tendency that the transporting force to transport the developer 3 is weak and thereby the cohesion of said developer takes place on the sleeve 1 and further the transportability remarkably lowers when a toner filming takes place. Further, uneven density in the form of lateral stripes synchronized with the moving speed of the developer layer sometimes occurs on the recorded image because developer located by a width of W eared with the magnetic field of a magnetic pole has affected the development at the developing position.